Azolla for rice production in Thailand

Summary

Thai farmers cannot apply chemical nitrogen fertilizers in the quantities recommended by the government because the price of rice is very low while the price of commercial fertilizers is relatively expensive. Azolla is very suitable as a source of nitrogen for rice in Thailand for the following reasons: the short time necessary for obtaining a substantial supply of nitrogen (as high as 3 kg N/ha/day), their N content (4–5%) and their tolerance of acidity and high temperature.

Azolla will not grow unless phosphate is supplied at the seeding time. Farmers must seed Azolla about 20 days before transplanting rice but in rainfed areas, there is insufficient time to seed Azolla before transplanting, due to the short period of water kept in the field. However, Azolla may be seeded between hills of rice plants immediately after transplanting. Because it is uneconomical to plow Azolla into the soil, Azolla may be allowed to decompose and release nitrogen slowly by natural decomposition processes.

One crop of Azolla whether added before or after transplanting gave yields which were almost equivalent to the 30 kg/ha of chemical nitrogen fertilizer. Two crops of Azolla seeded before and after transplanting gave the similar yield as in the 60 kg N/ha fertilized plot. There was no difference in grain yield, whether Azolla seeded after transplanting of rice was incorporated or not.